Ultrasonic sensor and electronic device

ABSTRACT

The ultrasonic sensor includes, on the same substrate, transmitter elements, receiver elements, a potential controller for receiver electrodes of the receiver elements, and a connection switching unit for the receiver electrodes and the potential controller. During the ultrasound transmission period of the transmitter elements, the connection switching unit connects the potential controller and the receiver electrodes. During the reception period of the receiver elements, the connection switching unit disconnects the potential controller and the receiver electrodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2010-101774 filed on Apr. 27, 2010. The entire disclosure of JapanesePatent Application No. 2010-101774 is hereby incorporated herein byreference.

BACKGROUND

1. Technical Field

The present invention relates to an ultrasonic sensor and to anelectronic device.

2. Related Art

One type of ultrasonic sensor known in the prior art has a transmitterelement for transmitting ultrasonic waves to a detection subject, andreceiver elements for receiving ultrasonic waves reflected from thedetection subject, the elements being disposed in an array on the samesubstrate (see Japanese Laid-Open Patent Application Publication No.2009-225419, for example).

The ultrasonic sensor disclosed in Japanese Laid-Open Patent ApplicationPublication No. 2009-225419 is provided with an oscillation isolationmember for compartmentalizing the transmitter element which transmitsultrasonic waves, and the receiver elements which receive ultrasonicwaves. This oscillation isolation member serves to inhibit transmissionof oscillation from the transmitter element to the receiver elementsduring ultrasound transmission, and to reduce reception of oscillationnoise by the receiver elements.

SUMMARY

According to the ultrasonic sensor disclosed in Japanese Laid-OpenPatent Application Publication No. 2009-225419, oscillation noise of thetransmitter element is reduced by the oscillation isolation member.However, because oscillation of the transmitter element duringultrasound transmission is greater than oscillation of the receiverelements during ultrasonic wave reception, oscillation noise cannot beeliminated to a sufficient extent, and the resultant problem isdiminished sensing accuracy of the received signal.

Specifically, in an ultrasonic sensor, when ultrasound is output from atransmitter element and the ultrasound that is reflected by an objectsuch as a detection subject is subsequently input to a receiver element,the ultrasound experiences attenuation and reduced sound pressure withgreater distance from the transmitter element to the object and greaterdistance from the object back to the receiver element. Such attenuationof ultrasound and reduced sound pressure is observed in reflection byobjects as well. Thus, the ultrasound input to the receiver element willhave lower sound pressure as compared with the ultrasound that wasoutput by the transmitter element, and for this reason it is typicalpractice to connect an amplifier to the receiver element, and to detectthe received signal based on ultrasound input to the receiver elementonce the signal has been amplified by the amplifier.

Consequently, despite reduced oscillation transmission from thetransmitter element through the use of an oscillation isolation member,if even slight oscillation reaches the receiver element, the signalproduced by the oscillation will be amplified and detected asoscillation noise. For this reason, it was difficult to distinguishbetween oscillation noise and a received signal produced by ultrasoundreflected by an object, resulting in diminished sensing accuracy ofreceived signals.

It is accordingly an object of the present invention to provide anultrasonic sensor and an electronic device able to afford reduceddetection of oscillation noise of the transmitter element and enhancedsensing accuracy of received signals.

An ultrasonic sensor according to a first aspect of the presentinvention has, on the same substrate, a transmitter element, whichincludes an transmission film adapted to transmit ultrasound throughoscillation, a transmission piezoelectric body for causing thetransmission film to oscillate, and a pair of actuation electrodes forapplying an actuation voltage to the transmission piezoelectric body;and a receiver element including a reception film adapted to oscillatethrough reception of the ultrasound, a reception piezoelectric body forconverting oscillation of the reception film to an electrical signal,and a pair of receiver electrodes for picking up the electrical signalthat is output from the reception piezoelectric body. The ultrasonicsensor includes a potential controller configured to bring the receiverelectrodes to a first potential, and a connection switching unitconfigured to switch a connection state of the receiver electrodes andthe potential controller. During the transmission period in which theultrasound is transmitted by the transmitter element, the connectionswitching unit being configured to switch to a first state in which thepotential controller and the receiver electrodes are connected. Duringthe reception period in which the ultrasound is received by thereception element, the connection switching unit being configured toswitch to a second state in which the potential controller and thereceiver electrodes are disconnected.

According to this ultrasonic sensor, when actuation voltage is appliedfrom the actuation electrodes to the transmission piezoelectric body inthe transmitter element, the transmission film oscillates due toexpansion and contraction of the transmission piezoelectric body, andultrasound is transmitted from the transmission film. In the receiverelement, ultrasound reflected from a detection subject is received bythe reception film, whereby the reception film oscillates. A potentialdifference is thereby created in the reception piezoelectric body, andan electrical signal based on the potential difference is output fromthe paired receiver electrodes.

According to this aspect, during the transmission period in whichultrasound is transmitted by the transmitter elements, the connectionswitching unit switches to a first state. The paired receiver electrodesand the potential controller are connected thereby, whereby the pairedreceiver electrodes are respectively brought to the same potential at afirst potential. Therefore, the potential difference of the pairedreceiver electrodes is zero, and the receiver electrodes do not outputan electrical signal. By so doing, during intervals of transmission ofultrasound by the transmitter elements, specifically, during intervalsin which the transmission film of the transmitter elements isoscillating, no electrical signal is output from the receiver electrodeseven if oscillation noise from the transmitter elements reaches thereceiver elements. Consequently, oscillation noise produced byoscillation of the transmitter elements is not detected.

During the reception period following completion of a transmissionperiod, on the other hand, the connection switching unit switches to thesecond state. Therefore, the receiver elements can receive only theultrasound received signals, and the sensing accuracy of the ultrasonicreceived signal can be enhanced.

As mentioned previously, in typical practice, an amplifier is connectedto the receiver element, and received signals based on ultrasound inputto the receiver element are detected after amplification by theamplifier. Oscillation noise generated by oscillation of thetransmission film of the transmitter element has amplitude several tensor several hundreds of times greater than ultrasonic received signalsinput to the receiver element. Therefore, if oscillation noise is inputto the amplifier, there is a risk of increased output voltage of theamplifier due to the amplified oscillation noise, resulting in increasedenergy consumption.

According to this aspect, during ultrasound transmission periods, thepaired receiver electrodes and the potential controller are connected,the potential difference of the paired receiver electrodes is zero, andno electrical signal is output by the receiver electrodes. Specifically,because the signal produced by oscillation noise is not input to theamplifier, amplification of oscillation noise and resultant higheroutput voltage can be prevented. Consequently, power consumption by theamplifier can be reduced.

In the ultrasonic sensor as described above, the connection switchingunit preferably has a potential control switch configured to switch theconnection state between the potential controller and at least one ofthe receiver electrodes, and a short switch connected to each of thereceiver electrodes and configured to switch the connection statebetween the receiver electrodes. In the first state, the connectionswitch portion is preferably configured to switch the short switch to aconnection state in which the receiver electrodes are connected, and toswitch the potential control switch to a connection state in which thepotential controller is connected to at least one of the receiverelectrodes.

According to this aspect, during transmission periods, the short switchshorts the paired receiver electrodes and, additionally, the potentialcontrol switch connects the potential controller to the paired receiverelectrodes, whereupon the potential controller respectively brings thepaired receiver electrodes to the same potential at a first potential.The potential difference of the paired receiver electrodes is therebybrought to zero. Specifically, because it is sufficient to simply shortthe paired receiver electrodes, the configuration can be simplified.

Moreover, because the paired receiver electrodes are shorted by theshort switch, the potential difference of the paired receiver electrodescan be reliably brought to zero, producing a state in which noelectrical signal is output from the receiver electrodes.

In the ultrasonic sensor as described above, the potential controllerpreferably has a first potential controller configured to apply avoltage to one of the receiver electrodes, and a second potentialcontroller configured to apply a voltage to the other of the receiverelectrodes. The connection switching unit preferably has a first switchconfigured to switch the connection state between the first potentialcontroller and the one of the receiver electrodes, and a second switchconfigured to switch the connection state between the second potentialcontroller and the other of the receiver electrodes. In the first state,the connection switching unit is preferably configured to switch thefirst switch to a connection state in which the first potentialcontroller and the one of the receiver electrodes are connected, and toswitch the second switch to a connection state in which the secondpotential controller and the other of the receiver electrodes areconnected.

According to this aspect, during transmission periods, the connectionswitching unit switches the first switch to a connection state in whichthe first potential controller and one receiver electrode are connected,and additionally switches the second switch to a connection state inwhich the second potential controller and the other receiver electrodeare connected. Therefore, the paired receiver electrodes and the firstand second potential controllers are connected, respectively bringingthe paired receiver electrodes to the same potential at a firstpotential. Therefore, the potential difference of the paired receiverelectrodes is zero, and no electrical signal is output from the receiverelectrodes. By so doing, during intervals in which the transmission filmof the transmitter elements is oscillating, no electrical signal isoutput from the receiver electrodes, even if oscillation noise from thetransmitter elements reaches the receiver elements. Consequently,oscillation noise produced by oscillation of the transmitter elements isnot detected.

During the reception period following completion of a transmissionperiod, on the other hand, the connection switching unit switches to thesecond state as described above. Therefore, the receiver elements canreceive only the ultrasound received signals, and the sensing accuracyof the ultrasonic received signal can be enhanced.

The ultrasonic sensor as described above preferably further includes atrigger signal generator configured to output a trigger signal at leastduring the transmission period, and an actuation controller configuredto output an actuation signal applied to the actuation electrodes of thetransmitter element while simultaneously activating the trigger signalgenerator. The connection switching unit is preferably configured toswitch to the first state upon input of the trigger signal from thetrigger signal generator, and to switch to the second state upontermination of input of the trigger signal.

According to this aspect, the actuation controller outputs an actuationsignal applied to paired actuation electrodes of the transmitterelements, while simultaneously activating the trigger signal generator.By so doing, the trigger signal generator is prompted to output atrigger signal. Subsequently, the connection switching unit, upon inputof the trigger signal, switches to the first state; and upon terminationof input of the trigger signal switches to the second state. Therefore,while the actuation controller is outputting an actuation signal to thetransmitter elements, the connection switching unit can be reliablyswitched to the first state, and the potential difference of the pairedreceiver electrodes can be brought to zero. Consequently, during thetransmission period, no electrical signal is output from the receiverelectrodes, and oscillation noise produced by oscillation of thetransmitter elements is not detected. During the reception periodfollowing completion of the transmission period, on the other hand, asdescribed previously, the receiver elements can receive only theultrasound received signals, and the sensing accuracy of the ultrasonicreceived signal can be enhanced.

In the ultrasonic sensor as described above, the trigger signalgenerator is preferably configured to output the trigger signal in atrigger output period equivalent to at least one cycle of the actuationsignal, plus the transmission period.

According to this aspect, the trigger output period is set to aninterval equivalent to at least one cycle of the ultrasonic actuationsignal transmitted by the transmitter element, plus the transmissionperiod.

There are instances in which oscillation noise generated during theultrasound transmission period reaches the receiver elements after thetransmission period has elapsed. According to the present invention, thetrigger signal continues to be output even after the transmission periodhas elapsed, and the potential difference of the paired receiverelectrodes remains at zero, whereby even if oscillation noise reachesthe receiver elements after the transmission period has elapsed, thereceiver elements do not output the oscillation noise as a receivedsignal. Consequently, the sensing accuracy of the ultrasonic receivedsignal by the receiver elements can be enhanced.

The electronic device according to another aspect includes theultrasonic sensor described above.

According to this aspect, by providing the ultrasonic sensor describedabove, there may be realized electronic devices with enhanced sensingaccuracy of the ultrasonic received signals as discussed above.

Whereas the prior art relied on providing an oscillation isolationmember discussed above, according to the present invention, thenecessity of providing such an oscillation isolation member is obviated,and accordingly the configuration can be simplified, making possibleapplication in devices requiring compact size, such as biologicaltesting devices, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is an exterior view of a biological testing device according to afirst embodiment of the invention.

FIG. 2 is a circuit block diagram depicting in model form an ultrasonicsensor in the first embodiment.

FIG. 3 is a cross sectional view of a transmitter element and a receiverelement in the first embodiment.

FIG. 4 is a graph showing a relationship of voltage of various signalsto time in the first embodiment.

FIG. 5 is a flowchart depicting operation of the ultrasonic sensor inthe first embodiment.

FIG. 6 is a circuit block diagram depicting in model form an ultrasonicsensor in a second embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

A first embodiment of the present invention is described below withreference to the drawings.

Configuration of Biological Testing Device

FIG. 1 is an exterior view showing a biological testing device 100 as anelectronic device according to a first embodiment of the invention.

As shown in FIG. 1, the biological testing device 100 is a devicedesigned to attach to a human finger using a band 120. The biologicaltesting device 100 includes a device main unit 110, and the band 120which is used to attach the device main unit 110 to the finger. Thebiological testing device 100 is also provided with an ultrasonic sensor10.

This biological testing device 100 is designed, for example, to bearranged with the finger contacting a contact surface 111, and totransmit ultrasound to the finger from the ultrasonic sensor 10 as wellas to receive ultrasound that is reflected from biological structures,such as blood vessels inside the finger, for example, for the purpose oftesting blood flow conditions, such as pulse or blood pressure, forexample, or to test some other biological condition.

Configuration of Ultrasonic Sensor

FIG. 2 is a circuit block diagram depicting in model form the ultrasonicsensor 10 in the first embodiment.

The ultrasonic sensor 10 is designed to transmit ultrasound to thefinger, as well as to receive ultrasound reflected from biologicalstructures such as blood vessels inside the finger, for example.

As shown in FIG. 2, the ultrasonic sensor 10 has a transmitter array 20and a receiver array 30 adjacent to the transmission array 20.

The transmitter array 20 is made up of an array structure in which aplurality of transmitter elements 21 are arranged along the horizontaldirection (the X axis direction in FIG. 2) and the vertical direction(the Y axis direction in FIG. 2). The receiver array 30 is made up of anarray structure in which a plurality of receiver elements 31 arearranged along the horizontal direction and the vertical direction.

The transmitter elements 21 are elements adapted to transmit ultrasoundon the basis of a transmission signal (actuating signal) that is inputfrom an actuation controller 14, discussed later. The receiver elements31 are elements adapted to receive ultrasound reflected from a detectionsubject or the like, and to convert ultrasound to an electrical signalfor output to the actuation controller 14.

According to the example shown here in FIG. 2, the ultrasonic sensor 10of the present embodiment has a configuration in which the plurality oftransmitter elements 21 and the plurality of receiver elements 31 areformed on a single sensor array substrate 11; however, this arrangementis not limiting. For example, in another possible arrangement, thetransmitter array 20 and the receiver array 30 have respective sensorarray substrates, and these sensor array substrates are fastened onto asingle sensor array substrate.

The sensor array substrate 11 is formed with generally rectangularshape, and is made of semiconductor-forming material such as silicon(Si), for example.

In addition to the arrays 20, 30, the ultrasonic sensor 10 is providedwith transmission amps 12 for amplifying the actuating signal which isinput to the transmitter elements 21; reception amps 13 for amplifyingthe received ultrasound signal received by the receiver elements 31; theactuation controller 14, which controls operation of the ultrasonicsensor 10; a potential controller 15 adapted to bring receiverelectrodes 3132, 3133 (described later) of the receiver elements 31 to afirst potential during a trigger output period Tr (see FIG. 4); and aconnection switching unit 16 for switching the connection state betweenthe potential controller 15 and the receiver electrodes 3132, 3133.

Configuration of Transmitter Elements

FIG. 3 is a cross sectional view depicting in model form a transmitterelement 21 and a receiver element 31 taken in cross section along thethickness direction of the sensor array substrate 11. In the drawingview of FIG. 3, the transmitter element 21 is shown at right in thedrawing. As shown in FIG. 3, the transmitter element 21 is provided witha support portion 211, a support film 212, and a transmissionpiezoelectric body 213.

The support portion 211 is a section that is formed at the locationwhere the transmitter element 21 is positioned on the sensor arraysubstrate 11. In this support portion 211 there is formed an openingportion 211A having, for example, a rectangular shape in plan view whenthe sensor array substrate 11 is viewed from a direction perpendicularto the plane of the sensor array substrate 11 (sensor plan view).

The diameter dimension D of the opening portion 211A is selectedappropriately within a range of about 100 μm to 200 μm, for example,depending on the natural frequency of a diaphragm 212A (transmissionfilm), discussed later. Ultrasound produced through oscillation of thisdiaphragm 212A is directed out towards the opening portion 211A.

The support film 212 obstructs the opening portion 211A. In the presentembodiment, this support film 212 is formed with a two-layerconfiguration. For example, where the support portion 211 is an Sisubstrate, an SiO₂ layer having a thickness dimension of 3 μm isproduced on the support portion 211 by a thermal oxidation process.Then, using a method such as sputtering or vapor deposition, a ZrO₂layer having a thickness dimension of 400 nm is produced over the SiO₂layer to form two layers.

The section where the opening portion 211A is obstructed by the supportfilm 212 constitutes the diaphragm 212A. The diaphragm 212A is a memberof thin film form, and through the opening portion 211A formed in thesupport portion 211 lies exposed to a space in the ultrasound outputdirection of the transmitter element 21 (in FIG. 3, downward in theplane of the page).

Similar to the opening portion 211A, the transmission piezoelectric body213 is a film-like member of rectangular shape in sensor plan view, forexample. This transmission piezoelectric body 213 is provided with apiezoelectric film 2131, and with actuation electrodes (a lowerelectrode 2132 and an upper electrode 2133) for applying voltage to thepiezoelectric film 2131.

The piezoelectric film 2131 is a film of PZT formed with a thicknessdimension of 1.4 μm, for example. According to the present embodiment,PZT is employed for the piezoelectric film 2131; however, any materialable to expand and contract in an in-plane direction through theapplication of electrical voltage may be used. Examples include leadtitanate (PbTiO₃), lead zirconate (PbZrO₃), or lead lanthanum titanate((Pb,La)TiO₃).

The lower electrode 2132 and the upper electrode 2133 are electrodesdisposed sandwiching the piezoelectric film 2131; the upper electrode2132 is formed with a thickness dimension of 200 nm on the face of thepiezoelectric film 2131 facing towards the diaphragm 212A, while theupper electrode 2133 is formed with a thickness dimension of 50 nm onthe back face side of the piezoelectric film 2131, i.e., side oppositethe face that faces towards the diaphragm 212A.

The upper electrodes 2133 and the lower electrodes 2132 of thetransmitter elements 21 apply a designated voltage to the piezoelectricfilm 2131 in response to an actuating signal input from the actuationcontroller 14.

Lower electrode lines 214 extending along the Y axis direction of thesensor array substrate 11 connect to the lower electrodes 2132, as shownin FIG. 2. Upper electrode lines 215 extending along the X axisdirection of the sensor array substrate 11 connect to the upperelectrodes 2133.

In this transmitter element 21, the piezoelectric film 2131 expands andcontracts in an in-plane direction through application of voltage acrossthe lower electrode 2132 and the upper electrode 2133. At this time, oneof the faces of the piezoelectric film 2131 is joined to the diaphragm212A via the lower electrode 2132, the upper electrode 2133 is formed onthe other face, and no additional layers are stacked over this upperelectrode 2133. For this reason, the piezoelectric film 2131 readilyexpands and contracts on the upper electrode 2133 side, but expands andcontracts only with difficulty on the diaphragm 212A side. Therefore,when voltage is applied to the piezoelectric film 2131, the film flexesinto a convex shape towards the opening portion 211A, inducing flexureof the diaphragm 212A. Consequently, by applying AC voltage to thepiezoelectric film 2131, the diaphragm 212A is caused to oscillate inthe film thickness direction, and ultrasound is output through thisoscillation of the diaphragm 212A.

Configuration of Receiver Elements

As noted previously, the receiver elements 31 have a configurationidentical to that of the transmitter elements 21, and therefore a briefdescription of the configuration will suffice.

In the drawing view of FIG. 3, the receiver element 31 is shown at leftin the drawing. This receiver element 31 is provided with a supportportion 311, a support film 312, and a reception piezoelectric body 313.The reception piezoelectric body 313 is provided with a piezoelectricfilm 3131 and with receiver electrodes (a lower electrode 3132 as one ofthe receiver electrodes, and an upper electrode 3133 as the otherreceiver electrode) for picking up an electrical signal (receivedsignal). The design of the receiver element 31 is such that whenultrasound reflected from a detection subject is received by a diaphragm312A (reception film), the diaphragm 312A oscillates in the filmthickness direction. In the receiver element 31, this oscillation of thediaphragm 312A gives rise to a potential difference between the face ofthe piezoelectric film 3131 on the lower electrode 3132 side thereof andthe face on the upper electrode 3133 side thereof. A received signalwhich reflects the amount of displacement of the piezoelectric film 3131is then output from the upper electrode 3133 and the lower electrode3132 to the actuation controller 14.

Configuration of Transmitter Array

As shown in FIG. 3, in the transmitter array 20, transmitter elements21, which are arranged along the X axis direction, have commonconnections to upper electrode lines 215 as described earlier, and theseupper electrode lines 215 are connected to transmission common electrodelines 216 which are disposed at the X direction ends of the transmitterarray 20.

Transmitter elements 21, which are arranged along the Y axis directionof the transmitter array 20, have common connections to the lowerelectrode lines 214, and are connected to transmission actuationelectrode lines 217 which are disposed in the −Y direction of thetransmitter array 20, for example. Here, because the transmitter array20 of the present embodiment is designed such that the ultrasound scansalong one direction (the X direction) while adjusting the transmissionangle, the lower electrode lines 214 have common connections with thetransmitter elements 21; however, in cases where ultrasound scans in atwo-dimensional direction, the lower electrode lines 214 may lead outfrom individual transmitter elements 21.

The transmission common electrode lines 216 and the transmissionactuation electrode lines 217 connect to the transmission amps 12. Thetransmission common electrode lines 216 are connected to ground (GND)through connection to a reference potential 17, and the upper electrodes2133 of the transmitter elements 21 are grounded. Meanwhile, thetransmission actuation electrode lines 217 input the actuation signalfrom the transmission amps 12 and apply an actuation voltage to thelower electrode 2132, thereby giving rise to a potential differencebetween the actuation electrodes 2132, 2133, and actuating thetransmitter elements 21.

Configuration of Transmitter Array

As shown in FIG. 2, in the receiver array 30 as in the transmitter array20, receiver elements 31, which are arranged along the X axis direction,have common connections to upper electrode lines 215, and these upperelectrode lines 215 are connected to reception common electrode lines316 which are disposed at the X direction ends of the receiver array 30.

Receiver elements 31, which are arranged along the Y axis direction ofthe receiver array 30, have common connections to the lower electrodelines 214, and are connected to reception detection electrode lines 317which are disposed in the −Y direction of the receiver array 30, forexample.

These reception common electrode lines 316 and reception detectionelectrode lines 317 connect to the reception amps 13. The amplitude(potential difference) of the received signal input to the receptioncommon electrode lines 316 and the reception detection electrode lines317 from the receiver electrodes 3132, 3133 of the receiver elements 31is amplified by the reception amps 13 to detect the frequency and otherproperties of the ultrasound received by the receiver elements 31.

Configuration of Transmission Amp and Reception Amp

The transmission amps 12 amplify the voltage value of the actuationsignal input from the actuation controller 14, and output the amplifiedactuation signal to the transmission actuation electrode lines 217.

The transmission amps 12 are connected to the transmission commonelectrode lines 216 (which are connected to the reference potential 17)and to the transmission actuation electrode lines 217. The receptionamps 13 input from the reception detection electrode lines 317 areceived signal that has been converted on the basis of the ultrasoundreceived by the receiver elements 31, then amplify the voltage value ofthe received signal and output it to the actuation controller 14. Thereception amps 13 are connected to the reception common electrode lines316 and to the reception detection electrode lines 317.

Configuration of Actuation Controller

The actuation controller 14 controls the actuation signal which is inputto the transmitter elements 21 of the ultrasonic sensor 10, and alsoprocesses the received signal which is output by the receiver elements31 of the ultrasonic sensor 10. As shown in FIG. 2, this actuationcontroller 14 is provided with an actuation signal generator 141 and asignal processor 142.

The actuation signal generator 141 is a circuit device that generates anactuation signal for output to the transmitter elements 21, and thatoutputs the signal to the transmission amps 12. Once the actuationsignal generator 141 outputs an actuation signal to the transmissionamps 12, a trigger signal generator 161, discussed later, is activated.Specifically, the actuation signal generator 141 generates an actuationsignal during individual burst cycles Tp (see FIG. 4), and outputs theactuation signal to the transmission amps 12 during a transmissionperiod Tt (see FIG. 4).

The signal processor 142 is a circuit device for processing the receivedsignals output by the receiver elements 21 and amplified by thereception amps 13. In the signal processor 142, pulse, blood pressure,or the like is calculated on the basis of the received signal frequency,for example.

Configuration of Connection Switching Unit

The connection switching unit 16 includes the trigger signal generator161, a potential control switch 162, and a short switch 163. During theoutput interval Tr of a trigger signal which is output by the triggersignal generator 161 (see FIG. 4), the connection switching unit 16switches to a first state in which the potential controller 15 and thereceiver electrodes 3132, 3133 are connected. Once the trigger outputperiod Tr has elapsed and the trigger signal has ceased, the connectionswitching unit 16 switches to a second state in which the potentialcontroller 15 and the receiver electrodes 3132, 3133 are disconnected.

Here, in the first state, the potential controller 15 applies negativevoltage to the receiver electrodes 3132, 3133 to bring them to a firstpotential at which the receiver electrodes 3132, 3133 are at the samepotential. The potential difference of the receiver electrodes 3132,3133 is therefore zero.

The trigger signal generator 161 is a circuit device that, onceactivated by the actuation signal generator 141 of the actuationcontroller 14, outputs a trigger signal to the potential control switch162 and to the short switch 163. The trigger signal generator 161 hasbeen set to output the trigger signal for a designated duration (thetrigger output period Tr in FIG. 4).

Referring to FIG. 4, optionally, the trigger output period Tr may be setto a duration longer than the transmission period Tt; specifically, setto a duration longer than the transmission period Tt by the equivalentof at least one cycle (one wavelength) of the actuation signal or more.According to the present embodiment, the trigger output period Tr is setto a duration longer than the transmission period Tt by the equivalentof approximately two cycles of the actuation signal. The upper limit forthe trigger output period Tr is computed using Equation (1) below.

$\begin{matrix}{{{Equation}\mspace{14mu} (1)}\mspace{619mu}} & \; \\{{Tr} < {2 \times \frac{Dtr}{C}}} & (1)\end{matrix}$

Here, c is the sound speed (m/s) of a medium, and Dtr is the distance(m) from the ultrasonic sensor 10 to a detection subject. This distanceDtr (m) is a designated value determined on the basis of the structureof the ultrasonic sensor 10 (the distance between the elements 21, 31and the sensor surface), and the detection subject (in the presentembodiment, blood vessels).

A micro switch or the like, for example, is employed as the potentialcontrol switch 162 which is connected to the reception common electrodelines 316 and to the potential controller 15. The potential controlswitch 162 is also connected to the reception common electrode lines316.

When a trigger signal is input from the trigger signal generator 161,the potential control switch 162 switches to a first state forconnecting the potential controller 15 and the reception commonelectrode lines 316. Thereby, negative voltage is applied to the upperelectrodes 3133 from the potential controller 15 via the receptioncommon electrode lines 316.

On the other hand, when input of the trigger signal ceases, thepotential control switch 162 switches to a second state for severing theconnection of the potential controller 15 and the reception commonelectrode lines 316. Thereby, negative voltage ceases to be applied tothe upper electrodes 3133.

Similar to the potential control switch 162, the short switch 163 mayemploy, for example, a micro switch or the like which is connected tothe reception common electrode lines 316 and the reception detectionelectrode lines 317. The electrode lines 316, 317 are connected to thereceiver electrodes 3132, 3133 and to the reception amps 13.

When a trigger signal is input from the trigger signal generator 161,the short switch 163 assumes a connection state for connecting thereception common electrode lines 316 and the reception detectionelectrode lines 317. The receiver electrodes 3132, 3133 are shortedthereby. As mentioned previously, the potential control switch 162applies negative voltage from the potential controller 15 to the upperelectrodes 3133 via the reception common electrode lines 316. Therefore,negative voltage from the potential controller 15 flows into thereception detection electrode lines 317 via the reception commonelectrode lines 316 and the short switch 163, and applied to the lowerelectrodes 3132.

The receiver electrodes 3132, 3133 are thereby brought to a firstpotential at which they have the same potential, and the potentialdifference of the receiver electrodes 3132, 3133 is zero.

Once the trigger signal ceases, the short switch 163 assumes a secondstate for severing the connection of the reception common electrodelines 316 and the reception detection electrode lines 317. Therefore,application of negative voltage to the lower electrodes 3132 ceases.

Operation of Ultrasonic Sensor

Operation of the ultrasonic sensor 10 is now described with reference tothe graph, shown in FIG. 4, depicting the relationship of voltage valuesof the various signals with time, and to the flowchart shown in FIG. 5.

First, the signal generator 141 of the actuation controller 14 generatesan actuation signal for output to the transmitter elements 21, andduring the transmission period Tt outputs the actuation signal to thetransmission amps 12 and activates the trigger signal generator 161.Thereby, during the trigger output period Tr, the trigger signalgenerator 161 outputs a trigger signal to the potential control switch162 and to the short switch 163 (Step S1).

Then, once the potential control switch 162 and the short switch 163input the trigger signal from the trigger signal generator 161, theswitches assume the first state whereby negative voltage is suppliedfrom the potential controller 15 to the reception common electrode lines316 and the reception detection electrode lines 317, and the receiverelectrodes 3132, 3133 assume a first potential at the same potential(Step S2).

Meanwhile, upon input of the actuation signal, the reception amps 12amplify the voltage value of the actuation signal, present the actuationsignal to the transmission actuation electrode lines 217, and applyactuation voltage to the lower electrodes 2132 of the transmitterelements 21 via the lower electrode lines 214. The upper electrodes 2133of the transmitter elements 21 are grounded through connection to thereference voltage 17 via the transmission common electrode lines 216.The transmitter elements 21 are thereby actuated through generation of apotential difference between the actuation electrodes 2132, 2133, andtransmit ultrasound (Step S3).

At this time, in the receiver array 30, negative voltage from thepotential controller 15 is supplied to the upper electrode lines 215 andthe lower electrode lines 214 via the reception common electrode lines316 and the reception detection electrode lines 317. Therefore, thereceiver electrodes 3132, 3133 of the receiver elements 31 assume afirst potential at the same potential, whereby their potentialdifference is zero and the receiver elements 31 do not output a receivedsignal. Specifically, as shown by the graph in FIG. 4, during triggeroutput periods Tr, negative voltage is applied to the receiverelectrodes 3132, 3133 of the receiver elements 31 and their potentialdifference goes to zero, and therefore a drop is observed in the graph.Consequently, even if oscillation of the diaphragm 212A reaches thereceiver elements 31 during transmission of ultrasound by thetransmitter elements 21, there is no flow of current to the receptioncommon electrode lines 316 and the reception detection electrode lines317. Therefore, the received signal is not amplified by the receptionamps 13, and output voltage is low.

Then, when the trigger output period Tr has elapsed, the trigger signalgenerator 161 ceases outputting the trigger signal (Step S4).

Once output of the trigger signal ceases in Step S4, the potentialcontrol switch 162 and the short switch 163 assume a second state inwhich their connection to the potential controller 15 is severed (StepS5).

At this time, because negative voltage from the potential controller 15is no longer supplied to the reception common electrode lines 316 andthe reception detection electrode lines 317, the receiver electrodes3132, 3133 assume a state in which a potential difference has arisen.Therefore, a received signal from the receiver electrodes 3132, 3133reflecting the amount of displacement of the piezoelectric film 3131 isinput to the reception amps 13 from the reception common electrode lines316 and the reception detection electrode lines 317. Then, as shown inthe graph in FIG. 4, the reception amps 13 amplify the voltage value ofthe received signal.

The received signal that was amplified by the reception amps 13 is theninput to the signal processor 142 of the actuation controller 14,whereupon the signal processor 142 performs signal processing of thereceived signal (Step S6). Thereby, in the signal processor 142, theamplitude, frequency, and other properties of the ultrasound received bythe receiver elements 31 are detected, and pulse, blood pressure, or thelike is computed.

The ultrasonic sensor 10 of the first embodiment described above affordsthe following advantages.

(1) During the transmission period Tt in which the transmitter elements21 transmit ultrasound, the connection switching unit 16 switches to thefirst state. The paired receiver electrodes 3132, 3133 and the potentialcontroller 15 are connected thereby, and the paired receiver electrodes3132, 3133 are brought to a first potential at the same respectivepotential. Therefore, the potential difference of the paired receiverelectrodes 3132, 3133 is zero, and no electrical signal is output by thepaired receiver electrodes 3132, 3133. Due to this design, during theinterval that the transmitter elements 21 are transmitting ultrasound,i.e., during the oscillation interval of the diaphragm 212A of thetransmitter elements 21, no electrical signal is output by the pairedreceiver electrodes 3132, 3133 even if oscillation noise from thetransmitter elements 21 reaches the receiver elements 31. Consequently,oscillation noise produced by oscillation of the transmitter elements 21is not detected.

On the other hand, during the reception period that follows elapse ofthe transmission period Tt, the connection switching unit 16 switches tothe second mode. Owing to this feature, the receiver elements 31 canonly receive ultrasound received signals, and the sensing accuracy ofthe ultrasonic received signal can be enhanced.

(2) During the ultrasound transmission period Tt, the paired receiverelectrodes 3132, 3133 and the potential controller 15 are connected, thepotential difference of the paired receiver electrodes 3132, 3133 iszero, and no electrical signal is output by the paired receiverelectrodes 3132, 3133. Specifically, no signal resulting fromoscillation noise is input to the reception amps 13, thereby preventinga rise in output voltage due to amplification of oscillation noise.Consequently, power consumption by the reception amps 13 can be reduced.

(3) During the transmission period Tt, the short switch 163 is promptedto short the paired receiver electrodes 3132, 3133, and additionally thepotential control switch 162 is prompted to connect the potentialcontroller 15 and the paired receiver electrodes 3132, 3133, whereby thepotential controller 15 brings the paired receiver electrodes 3132, 3133to a first potential at the same respective potential. The potentialdifference of the paired receiver electrodes 3132, 3133 is thereforezero. That is, because it suffices to merely short the paired receiverelectrodes 3132, 3133, the configuration can be simplified.

(4) The actuation controller 14 outputs an actuation signal forapplication to the paired receiver electrodes 2132, 2133 of thetransmitter elements 21, and simultaneously activates the trigger signalgenerator 161. The trigger signal generator 161 thereby outputs atrigger signal. When the connection switching unit 16 inputs the triggersignal, it switches to the first state; and when input of the triggersignal ends, it switches to the second state. Owing to this feature,during output of the actuation signal to the transmitter elements 21 bythe actuation controller 14, the connection switching unit 16 can bereliably switched to the first state, and the potential difference ofthe paired receiver electrodes 3132, 3133 can be brought to zero.Consequently, during the transmission period Tt, no electrical signal isoutput from the receiver electrodes 3132, 3133, and oscillation noisegenerated by oscillation of the transmitter elements 21 is not detected.Further, during the reception period following completion of thetransmission period Tt, as described previously, the receiver elements31 are able to receive only ultrasound received signals, and the sensingaccuracy of the ultrasonic received signal can be enhanced.

(5) The trigger output period Tr is set to an interval of durationequivalent to at least one cycle of the ultrasonic actuation signaltransmitted from the transmitter elements 21, plus the transmissionperiod Tt.

There are instances in which oscillation noise generated during theultrasound transmission period Tt reaches the receiver elements 31 afterthe transmission period has elapsed Tt. According to the presentembodiment, the trigger signal continues to be output even after thetransmission period Tt has elapsed, and the potential difference of thepaired receiver electrodes 3132, 3133 remains at zero, whereby even ifoscillation noise reaches the receiver elements 31 after thetransmission period Tt has elapsed, the receiver elements 31 do notoutput the oscillation noise as a received signal. Consequently, thesensing accuracy of the ultrasonic received signal by the receiverelements 31 can be enhanced.

(6) The biological testing device 100 provided with the ultrasonicsensor 10 described above is disposed with the contact surface 111contacting the finger or the like, whereupon ultrasound is transmittedto blood vessels. In this case, the contact surface 111 and the bloodvessels are in mutually proximate locations. Where the detection subjectis situated at a location close to the ultrasonic sensor 10 in this way,by shortening the trigger output period Tr, rapid switching between thefirst state and the second state can take place, and sensing of thedetection subject close by is possible.

Second Embodiment

FIG. 6 is a circuit block diagram depicting in model form an ultrasonicsensor 10 in a second embodiment.

The differences are that, whereas according to the preceding firstembodiment, the connection switching unit 16 has a configurationprovided with the potential control switch 162 and the short switch 163,the potential controller 16 according to the second embodiment isprovided with a first switch 164 and a second switch 165 in place of theshort switch 163; and the potential controller 15 is provided with afirst potential controller 18 and a second potential controller 19respectively connected to the first switch 164 and the second switch165.

The first switch 164 has a configuration comparable to the potentialcontrol switch 162 in the preceding embodiment, and is adapted to switchthe connection state of the first potential controller 18 and thereception detection electrode lines 317 connected to the lowerelectrodes 3132.

The second switch 165 has a configuration comparable to the potentialcontrol switch 162 in the preceding embodiment, and is adapted to switchthe connection state of the second potential controller 19 and thereception common electrode lines 316 connected to the upper electrodes3133.

The first potential controller 18 applies negative voltage to the lowerelectrodes 3132, while the second potential controller 19 appliesnegative voltage to the upper electrodes 3133.

Input of a trigger signal from the trigger signal generator 161 sets upa first state in which the first switch 164 connects the first potentialcontroller 18 with the reception detection electrode lines 317, and thesecond switch 165 connects the second potential controller 19 with thereception common electrode lines 316. This sets up a state in whichnegative voltage is applied to the paired receiver electrodes 3132, 3133from the potential controllers 18, 19. The paired receiver electrodes3132, 3133 are thereby brought to a first potential at the samepotential, and the potential difference of the paired receiverelectrodes 3132, 3133 is zero.

On the other hand, when input of the trigger signal ceases, the firstswitch 164 and the second switch 165 assume a second state in which thefirst potential controller 18 is disconnected from the receptiondetection electrode lines 317, and the second potential controller 19 isdisconnected from the reception common electrode lines 316. As a result,negative voltage ceases to be applied to the paired receiver electrodes3132, 3133.

The second embodiment described above affords advantages comparable toadvantages (1), (2), and (4) to (6) of the preceding first embodiment.

Additionally, in the present embodiment, during the transmission periodTt the connection switching unit 16 switches the first switch 164 to aconnection state for connecting the lower electrodes 3132 to the firstpotential controller 18, and additionally switches the second switch 165to a connection state for connecting the upper electrodes 3133 to thesecond potential controller 19. The paired receiver electrodes 3132,3133 are thereby connected with the first and second potentialcontrollers 18, 19, and the paired receiver electrodes 3132, 3133 arerespectively brought to the same potential at a first potential.Therefore, the potential difference of the paired receiver electrodes3132, 3133 is zero, and no electrical signal is output from the receiverelectrodes 3132, 3133. Owing to this feature, during the oscillationinterval of the diaphragm 212A of the transmitter elements 21, noelectrical signal is output from the paired receiver electrodes 3132,3133 even if oscillation noise from the transmitter elements reaches thereceiver elements 31. Consequently, oscillation noise generated byoscillation of the transmitter elements 21 is not detected.

On the other hand, during the reception period following elapse of thetransmission period Tt, as described previously, the connectionswitching unit 16 switches to the second state. The receiver elements 31thereby can receive only ultrasound received signals, and the sensingaccuracy of the ultrasonic received signal can be enhanced.

Modifications of the Embodiments

While certain preferred configurations, methods, and the like forembodying the present invention have been shown herein, these are notintended as limiting of the invention.

In the preceding embodiments, negative voltage is applied to the pairedreceiver electrodes 3132, 3133 from the potential controllers 15, 18, 19to bring the paired receiver electrodes 3132, 3133 to a first potential;however, optionally, the potential controllers 15, 18, 19 may be set toreference potential, and the paired receiver electrodes 3132, 3133brought to the first potential by being grounded.

In this case, the configuration may omit the potential control switch162 of the first embodiment, and keep the upper electrodes 3133 groundedat all times to the potential controller 15. Likewise, in the secondembodiment, the configuration may omit the second switch 165, and keepthe upper electrodes 3133 grounded at all times to the second potentialcontroller 19. This affords a configuration in which only the shortswitch and the first switch 164 are controlled, and the configurationcan be simplified.

In the preceding embodiments, the trigger signal is output during thetrigger output period Tr; however, optionally, transmission may takeplace during the transmission period Tt only, or the duration of thetrigger output period Tr may be set appropriately depending on thedistance to the detection subject.

In the preceding embodiments, the actuation controller 14 and theconnection switching unit 16 are configured separately, but aconfiguration incorporating the actuation controller 14 into theconnection switching unit 16 is also possible. With this configuration,the trigger signal generator 161 will output a trigger signal once theactuation signal generator 141 generates an actuation signal, and theresponse of the trigger signal generator 161 can be improved. Also,while the trigger signal generator 161 is part of the connectionswitching unit 16, optionally, it may be part of the actuationcontroller 14 instead. In yet another possible configuration, thetrigger signal generator 161 is omitted, and a trigger signal isgenerated during generation of the actuation signal by the actuationsignal generator 141.

While preceding embodiments describe an example of a biological testingdevice as the electronic device, no limitation thereto is imposed; forexample, devices adapted to sense distance between vehicles, or devicesfor measuring flow rate or flow speed of a fluid through piping, and thelike may also be given as examples.

General Interpretation of Terms

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts. Finally, terms of degree such as“substantially”, “about” and “approximately” as used herein mean areasonable amount of deviation of the modified term such that the endresult is not significantly changed. For example, these terms can beconstrued as including a deviation of at least ±5% of the modified termif this deviation would not negate the meaning of the word it modifies.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents.

1. An ultrasonic sensor comprising: a substrate, a transmitter elementformed above the substrate, the transmitter element including antransmission film adapted to transmit ultrasound through oscillation, atransmission piezoelectric body for causing the transmission film tooscillate, and a pair of actuation electrodes for applying an actuationvoltage to the transmission piezoelectric body; a receiver elementformed above the substrate, the receiver element including a receptionfilm adapted to oscillate through reception of the ultrasound, areception piezoelectric body for converting oscillation of the receptionfilm to an electrical signal, and a pair of receiver electrodes forpicking up the electrical signal that is output from the receptionpiezoelectric body; a potential controller configured to bring thereceiver electrodes to a first potential; and a connection switchingunit configured to switch a connection state of the receiver electrodesand the potential controller, during a transmission period in which theultrasound is transmitted by the transmitter element, the connectionswitching unit being configured to switch to a first state in which thepotential controller and the receiver electrodes are connected, andduring a reception period in which the ultrasound is received by thereception element, the connection switching unit being configured toswitch to a second state in which the potential controller and thereceiver electrodes are disconnected.
 2. The ultrasonic sensor accordingto claim 1, wherein the connection switching unit has a potentialcontrol switch configured to switch the connection state between thepotential controller and at least one of the receiver electrodes, and ashort switch connected to each of the receiver electrodes and configuredto switch the connection state between the receiver electrodes, and inthe first state, the connection switching unit is configured to switchthe short switch to a connection state in which the receiver electrodesare connected, and to switch the potential control switch to aconnection state in which the potential controller is connected to atleast one of the receiver electrodes.
 3. The ultrasonic sensor accordingto claim 1, wherein the potential controller has a first potentialcontroller configured to apply a voltage to one of the receiverelectrodes, and a second potential controller configured to apply avoltage to the other of the receiver electrodes, the connectionswitching unit has a first switch configured to switch the connectionstate between the first potential controller and the one of the receiverelectrodes, and a second switch configured to switch the connectionstate between the second potential controller and the other of thereceiver electrodes, and in the first state, the connection switchingunit is configured to switch the first switch to a connection state inwhich the first potential controller and the one of the receiverelectrodes are connected, and to switch the second switch to aconnection state in which the second potential controller and the otherof the receiver electrodes are connected.
 4. The ultrasonic sensoraccording to claim 1, further comprising a trigger signal generatorconfigured to output a trigger signal at least during the transmissionperiod, and an actuation controller configured to output an actuationsignal applied to the actuation electrodes of the transmitter elementwhile simultaneously activating the trigger signal generator, theconnection switching unit being configured to switch to the first stateupon input of the trigger signal from the trigger signal generator, andto switch to the second state upon termination of input of the triggersignal.
 5. The ultrasonic sensor according to claim 4, wherein thetrigger signal generator is configured to output the trigger signal in atrigger output period equivalent to at least one cycle of the actuationsignal, plus the transmission period.
 6. An ultrasonic sensorcomprising: a substrate having a plurality of opening portions; asupport film covering the opening portions; a first piezoelectricelement formed above the support film and in the inside region of afirst opening portion among the opening portions in plan view; a secondpiezoelectric element formed above the support film and in the insideregion of a second opening portion among the opening portions in planview; a potential controller configured to supply a potential; and aconnection switching unit configured to switch a connection state of thefirst piezoelectric element and the potential controller, the firstpiezoelectric element including a piezoelectric body and a pair of firstpiezoelectric element electrodes connected to the piezoelectric body,during at least part of duration of a transmission period in which anactuation voltage is applied to the second piezoelectric element, theconnection switching unit being configured to switch to a first state inwhich the potential controller and the first piezoelectric elementelectrodes are connected, and during at least part of duration of areception period in which an electrical signal of the firstpiezoelectric element is picked up, the connection switching unit beingconfigured to switch to a second state in which the potential controllerand at least one of the first piezoelectric element electrodes aredisconnected.
 7. The ultrasonic sensor according to claim 6, wherein theconnection switching unit includes a potential control switch configuredto switch the connection state between the potential controller and atleast one of the first piezoelectric element electrodes, and a shortswitch connected to each of the first piezoelectric element electrodesand configured to switch the connection state between the firstpiezoelectric element electrodes, and in the first state, the connectionswitching unit is configured to switch the short switch to a connectionstate in which the first piezoelectric element electrodes are connected,and to switch the potential control switch to a connection state forconnecting the potential controller to at least one of the firstpiezoelectric element electrodes.
 8. The ultrasonic sensor according toclaim 6, wherein the potential controller includes a first potentialcontroller and a second potential controller, and the connectionswitching unit includes a first switch configured to switch theconnection state between the first potential controller and one of thefirst piezoelectric element electrodes, and a second switch configuredto switch the connection state between the second potential controllerand the other of the first piezoelectric element electrodes, and, in thefirst state, the connection switching unit is configured to switch thefirst switch to a connection state for connecting the first potentialcontroller to the one of the first piezoelectric element electrodes, andto switch the second switch to a connection state for connecting thesecond potential controller to the other of the first piezoelectricelement electrodes.
 9. The ultrasonic sensor according to claim 6,further comprising a trigger signal generator configured to output atrigger signal at least during the transmission period, and an actuationcontroller configured to output an actuation signal to the secondpiezoelectric element while simultaneously activating the trigger signalgenerator, the connection switching unit being configured to switch tothe first state upon input of the trigger signal from the trigger signalgenerator, and to switch to the second state upon termination of inputof the trigger signal.
 10. The ultrasonic sensor according to claim 9,wherein the trigger signal generator is configured to output the triggersignal for a trigger output period of duration equivalent to at leastone cycle of the actuation signal, plus the transmission period.
 11. Anelectronic device including the ultrasonic sensor according to claim 1.12. An electronic device including the ultrasonic sensor according toclaim
 2. 13. An electronic device including the ultrasonic sensoraccording to claim
 3. 14. An electronic device including the ultrasonicsensor according to claim
 4. 15. An electronic device including theultrasonic sensor according to claim
 5. 16. An electronic deviceincluding the ultrasonic sensor according to claim
 6. 17. An electronicdevice including the ultrasonic sensor according to claim
 7. 18. Anelectronic device including the ultrasonic sensor according to claim 8.19. An electronic device including the ultrasonic sensor according toclaim
 9. 20. An electronic device including the ultrasonic sensoraccording to claim 10.